Briefly, it works. For most people this is a curiosity, but free AT&T cell calls to Montreal will pay for my iPhone.

Which explains this mysterious meeting transcript I found in my junk mail today:

... AT&T guy: "Thanks for joining us today. We really admire the work you've done at Google. We know you appreciate the fiber services we provide, and you understand why it's only fair that Google pay a bit more for the quality of service only we can provide."